Study monitors DNA breaks and chromosome translocations in real time

August 9, 2013 by Lin Edwards, Medical Xpress report
A chromosome translocation is visualized in living cells by the colocalization of chromosome breaks marked with differently colored fluorescent proteins (green, red). Credit: Vassilis Roukos

(Medical Xpress)—Researchers in the U.S. have developed a new method to study damage to DNA and resultant translocations in living cells.

DNA damage occurs regularly in living cells as a result of normal cellular processes and because of environmental factors such as radiation. The damage is constantly repaired, but if the repairs fail a break may occur in the two DNA strands and the two sections of the then drift apart. This is referred to as a double-strand break (DSB), and is dangerous to the host cell because when the broken strands attempt to pair off again they have no template to follow and can pair with different chromosomes, producing a chromosome translocation, which is an unexpected rearrangement of the genes. Chromosome translocations are a hallmark of .

Researcher Vassilis Roukos, of the National Cancer Institute in Bethesda, Maryland, and colleagues used ultra-high throughput time-lapse to monitor chromosome translocations in real time. The team's aim was to study the events during and after translocations in order to increase our understanding of these processes, and they succeeded in capturing images of DSBs and other translocation events as they occurred.

The team used living with their DNA molecules engineered to split when exposed to a specific enzyme. They used fluorescent proteins to tag the broken ends and then used their microscope time-lapse imaging system to watch what happened over the next 36 hours.

A chromosome translocation visualized in 3D. The translocation is visualized by the colocalization of chromosome breaks marked with differently colored fluorescent proteins (green, red). DNA is stained cyan. Credit: Vassilis Roukos

They found that there were three distinct phases in chromosome translocation. The first was the DNA segments moving around a little, in an apparent random search for a "partner" for the broken strands to pair with; the second was for two broken segments to line up, and the third was for the segments to join together. In most instances, the DSB segments immediately joined up with the correct partner, but on rare occasions two DSBs of different chromosomes paired instead. Co-author Tom Misteli, also of the National Cancer Institute, said these translocations are rare, being seen in only one in around every 300 cells.

The researchers also discovered that chromosome translocations commonly occurred within hours of the double-strand breaking, and that their occurrence was unrelated to the cell cycle.

Another finding was that the cell's DNA repair system enzymes had an influence on the formation of translocations. For example, when the researchers disabled one of these enzymes, DNA-dependent protein kinase (DNAPK) in some of the cells, a chromosome translocation was nearly 10 times as likely to occur than in cells with active DNAPK. Misteli said that while DNAPK was previously known to play a role in translocation formation, little was understood about how it operates, and the new study was able to shed more light on the processes involved. One finding was that the incorrect strands still line up when DNAPK is disabled, but they are much less likely to join together, indicating that DNAPK is necessary to prevent incorrect pairings.

Misteli said the next step in the research is to try to find ways of preventing the DNA repairs from going wrong. The paper was published on 9 August in the journal Science.

Explore further: Scientists resolve how chromosomal mix-ups lead to tumors

More information: Spatial Dynamics of Chromosome Translocations in Living Cells, Science 9 August 2013: Vol. 341 no. 6146 pp. 660-664 DOI: 10.1126/science.1237150

Chromosome translocations are a hallmark of cancer cells. We have developed an experimental system to visualize the formation of translocations in living cells and apply it to characterize the spatial and dynamic properties of translocation formation. We demonstrate that translocations form within hours of the occurrence of double-strand breaks (DSBs) and that their formation is cell cycle–independent. Translocations form preferentially between prepositioned genome elements, and perturbation of key factors of the DNA repair machinery uncouples DSB pairing from translocation formation. These observations generate a spatiotemporal framework for the formation of translocations in living cells.

Related Stories

Scientists resolve how chromosomal mix-ups lead to tumors

March 29, 2012
(Medical Xpress) -- A new study by scientists from the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), part of the National Institutes of Health, resolves longstanding questions about ...

Abnormal DNA maintenance related to cancer

December 10, 2012
DNA, like houses and cars, needs ongoing maintenance. Rays of ultraviolet sunlight, chemical pollutants and normal biochemical processes in the cell can damage it. Cells routinely repair this damage before making proteins ...

New technique identifies first events in tumor development

September 29, 2011
A novel technique that enables scientists to measure and document tumor-inducing changes in DNA is providing new insight into the earliest events involved in the formation of leukemias, lymphomas and sarcomas, and could potentially ...

To understand chromosome reshuffling, look to the genome's 3D structure

February 16, 2012
That our chromosomes can break and reshuffle pieces of themselves is nothing new; scientists have recognized this for decades, especially in cancer cells. The rules for where chromosomes are likely to break and how the broken ...

Chromosomal translocations point the way toward personalized cancer care

August 13, 2012
A broken chromosome is like an unmoored beansprout circling in search of attachment. If a cell tries to replicate itself with broken chromosomes, the cell will be killed and so it would very much like to find its lost end. ...

Recommended for you

More surprises about blood development—and a possible lead for making lymphocytes

January 22, 2018
Hematopoietic stem cells (HSCs) have long been regarded as the granddaddy of all blood cells. After we are born, these multipotent cells give rise to all our cell lineages: lymphoid, myeloid and erythroid cells. Hematologists ...

How metal scaffolds enhance the bone healing process

January 22, 2018
A new study shows how mechanically optimized constructs known as titanium-mesh scaffolds can optimize bone regeneration. The induction of bone regeneration is of importance when treating large bone defects. As demonstrated ...

Bioengineered soft microfibers improve T-cell production

January 18, 2018
T cells play a key role in the body's immune response against pathogens. As a new class of therapeutic approaches, T cells are being harnessed to fight cancer, promising more precise, longer-lasting mitigation than traditional, ...

Weight flux alters molecular profile, study finds

January 17, 2018
The human body undergoes dramatic changes during even short periods of weight gain and loss, according to a study led by researchers at the Stanford University School of Medicine.

Secrets of longevity protein revealed in new study

January 17, 2018
Named after the Greek goddess who spun the thread of life, Klotho proteins play an important role in the regulation of longevity and metabolism. In a recent Yale-led study, researchers revealed the three-dimensional structure ...

The HLF gene protects blood stem cells by maintaining them in a resting state

January 17, 2018
The HLF gene is necessary for maintaining blood stem cells in a resting state, which is crucial for ensuring normal blood production. This has been shown by a new research study from Lund University in Sweden published in ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Aug 11, 2013
Scientists discover that DNA damage occurs as part of normal brain activity
A non harmful effect when repair is successful. An alleged process of memory and learning.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.